This invention relates to alarm signal generators and more particularly to integrated circuit (IC) alarm signal generating circuits for producing from a speaker sharp repeating yelping or whooping sounds.
Such a yelping sound is known to be unpleasant and to instill in those within earshot a sense of danger and alarm. Acoustic alarms of this type are useful in alarm systems designed to detect smoke and fire, clandestine intruders and the presence of poisonous gasses, inter alia.
It is known to generate yelp alarm sounds by driving a voltage controlled oscillator (VCO)12 with a periodic ramp voltage from a ramp generator circuit 14 as illustrated in FIG. 1. The output of the VCO 12 is connected to an IC driver or power amplifier 17 that drives a speaker 18. In integrated circuit form, each of these two oscillator circuits 12 and 14 normally requires at least one discrete capacitor connected to the integrated circuit. Such discrete capacitors 15 and 16 are typically much larger and more expensive than the integrated circuit portion of the system.
It is an object of this invention to provide a yelping type IC alarm generator that requires only one external capacitor.
It is a parallel object of this invention to provide such a generator having only one oscillator.
It is a further object of this invention to provide a low cost yelping alarm signal generator.